1. Technical Field
The present invention relates to a mask correction method that combines correction using a focused ion beam and correction using an electron beam, and to a device realizing this.
2. Related Art
So-called transparent defect correction for repairing defect sections of a mask used in semiconductor manufacturing processes, and so-called opaque defect correction for removing additional sections are carried out using technology such as deposition carried out by irradiating a focused ion beam (FIB) while spraying a source material gas, and sputter etching and gas assisted etching for irradiating a focused ion beam. Currently, this technology is established in the field of FIB mask repair. However, gallium, which is a liquid metal, is generally used as the ion material for this focused ion beam, and there is a problem that the sample surface is damaged by Ga ions irradiated In the course of processing. Accordingly, since at a coarse processing stage processing is carried out at a high acceleration voltage, a procedure is necessary to carefully perform finishing processing of a sample surface that has been subjected to damage because of this high acceleration voltage with a low acceleration voltage at the finishing processing stage, and polish the damaged sample surface. Although it is possible to repair the roughened sample surface using this procedure, since gallium is used as the ion material, the gallium is injected into a mask, which is the sample, and this injected gallium remains in the finished mask. When this mask is used in lithography, the remaining gallium absorbs light and adversely affects transparency, and causes an imbalance in intensity of light irradiated to resist. Because the latest semiconductor patterns are becoming extremely detailed, it is necessary to use light of short wavelength as a light source in order to obtain a clear transfer image. The problem of this light absorption is therefore particularly serious when using light at a wavelength of 157 nm.
Recently, photolithography using phase shift masks in order to increase mask resolution has been widely used in the manufacture of semiconductor circuits. This lithography is intended to improve mask resolution using phase difference of light as well as light amplitude distribution. One example of a photolithography method (phase shift method) using a phase shift mask is shown in FIG. 6a, FIG. 6B, FIG. 6C and FIG. 6D. FIG. 6A is a cross sectional drawing of a phase shift mask, having a shaded pattern formed on the surface of a glass substrate 23 using Cr. A subsequent shaded pattern 62 is formed extremely close to one shaded pattern, and an open section 44 is formed between adjacent shaded patterns. These are repeatedly formed in the same manner. Also, a transparent film is formed in every other open section 44, and this is called a phase shifter film 42. The material of the phase shifter film 42 is a transparent material, and can be an inorganic material such as magnesium fluoride, titanium dioxide or silicon dioxide, or an organic material such as a polymer. It is also useful to use a resist material for the phase shift film 42.
In FIG. 6A, coherent light irradiated from above passes through each open section 44, and binds an image on the wafer either directly or via a lens optical system. Light passing through the phase shifter film 42 has light phase shifted by 180° compared to the light that has not passed through the phase shifter film. Amplitude distribution of light passing through the mask open sections is as shown in FIG. 6B. Specifically, light that has passed through open sections 44 in the phase shifter film 42 and light that has passed through open sections 44 that are not in the phase shifter film 42 are 180° out of phase with each other. Also, since light that has passed through the open sections 44 is diffracted, diffracted light also reaches the wafer corresponding to sections in the shadow of the shaded pattern 62. Therefore, amplitude (strength) of light reaching the wafer is as shown in FIG., 6C. Light diffracted at shadow sections of a particular shaded pattern 62 and rotated from left and right open sections is 180° out of phase with each other. That is, negating this, the strength distribution of light irradiated on the wafer becomes as shown in FIG. 6D. Specifically, an image of the open section is clearly separated. Also, besides the phase shifter film, there is also a method of forming a groove 45 in the glass substrate and causing phase shift, as shown in FIG. 6E.
With respect to the mask correction method, not only techniques such as CVD and etching using an FIB, but also CVD and gas assisted etching using an electron beam as an energy beam are disclosed in previous patents. For example, patent document 1 (Japanese Patent Laid-open No. Hei. 4-125642) shows a technique, intended to correct defects occurring in a transparent film of a photo mask used for phase shift with high precision, wherein gas for CVD is attached to a main surface of a photomask, and a correction film is then deposited onto the defect regions by selectively irradiating an energy beam to the defect regions. Also disclosed is, after causing etching gas to be attached to the main surface of the photomask, etching the defect regions by selectively irradiating the defect regions with an energy beam. Further, there is disclosed deposition of a transparent film by selective irradiation of the energy beam on part of a transparent region of the main surface of the photomask, for the purpose of forming a transparent film on the main surface of a phase shift photomask. Here, a focused ion beam and an electron beam are included as examples of the energy beam.
Patent document 2 (Japanese Patent Laid-open No. Hei. 5-114336) discloses a technique of etching defect sections of a phase shift mask until the defect sections become a substantially flat thin film, and then changing a refractive index of a phase shifter of the defect regions that have been substantially flattened by carrying out ion implantation by irradiation of an ion beam so that there is no phase difference, and also discloses a method of irradiating a heat energy beam such as an electron beam to change a refractive index by causing thermal strain, for the purpose of carrying out correction to defects of a phase shifter of a phase shifter mask simply and with high precision Also, patent document 3 (Japanese Patent Laid-open No. Hei. 6-42069) discloses a technique of irradiating an electron beam in a material gas atmosphere to correct missing defects by forming a shading film on the correction regions, for the purpose of enabling correction of missing defects of a photomask in a short time.
However, even though a technique for changing refractive index by gas assisted etching or CVD using an electron beam, or by causing thermal strain, are disclosed in the above patent documents, there is neither direct disclosure of damage caused by gallium ions of an FIB, the effect of gallium ions remaining in a mask, and removing the effect by separately using an ion beam and an electron beam taking into consideration differences in their characteristics, and the technical concept of providing a mask repair device in mask correction provided with two lens barrels to compensate for the drawbacks by using two separate beams, nor any suggestion of any recognition of these problems.
Patent document 1: Japanese Patent Laid-open No. Hei. 4-125642, FIG. 1, FIG. 2, FIG. 7 and FIG. 8.
Patent document 2: Japanese Patent Laid-open No. Hei. 5-114336, claim 6 and paragraph [0037].
Patent document 3: Japanese Patent Laid-open No. Hei. 6-42069, page 4 column 7, line 44-column 8, line 4.